Unsupported query: greatest(): expected avg() to be of type float, found type decimal

[Tim Graham]

It looks like the GREATEST function can't compare mixed number types:

SELECT ... GREATEST(AVG("aggregation_book"."rating"), AVG("aggregation_book"."price")) AS "price_or_median"
FROM "aggregation_publisher"
LEFT OUTER JOIN "aggregation_book" ON ("aggregation_publisher"."id" = "aggregation_book"."publisher_id")
GROUP BY "aggregation_publisher"."id"
HAVING GREATEST(AVG("aggregation_book"."rating"), AVG("aggregation_book"."price")) >= ("aggregation_publisher"."num_awards")
ORDER BY "aggregation_publisher"."num_awards" ASC;

rating is FloatField
price is DecimalField

Django test failure:

======================================================================
ERROR: test_expression_on_aggregation (aggregation.tests.AggregateTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/tim/code/django/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
psycopg2.errors.InvalidParameterValue: greatest(): expected avg(price) to be of type float, found type decimal


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/tim/code/django/tests/aggregation/tests.py", line 1100, in test_expression_on_aggregation
    qs, [1, 3, 7, 9], lambda v: v.num_awards)
  File "/home/tim/code/django/django/test/testcases.py", line 1047, in assertQuerysetEqual
    items = map(transform, qs)
  File "/home/tim/code/django/django/db/models/query.py", line 274, in __iter__
    self._fetch_all()
  File "/home/tim/code/django/django/db/models/query.py", line 1242, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/home/tim/code/django/django/db/models/query.py", line 55, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
  File "/home/tim/code/django/django/db/models/sql/compiler.py", line 1100, in execute_sql
    cursor.execute(sql, params)
  File "/home/tim/code/django/django/db/backends/utils.py", line 99, in execute
    return super().execute(sql, params)
  File "/home/tim/code/django/django/db/backends/utils.py", line 67, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/home/tim/code/django/django/db/backends/utils.py", line 76, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/home/tim/code/django/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/tim/code/django/django/db/utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/home/tim/code/django/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
django.db.utils.DataError: greatest(): expected avg(price) to be of type float, found type decimal